Vessels, pipes, condensers and boilers used in the chemical & food processing industries, power plants, oil field operations are subject to the formation of scale, which interferes with functioning. The word “scale” when used herein includes any solid deposit formed on a solid ferriferous metal surface as a result of contact between the metal surface and an aqueous solution in liquid or vapor state. During use, water storage tanks, conduits, plumbing, cooling towers, process equipment, electrolysis membranes and other units develop scale which must be removed, preferably dissolved. Typically, this scale is removed using an acid solution, generally a solution of hydrochloric acid. To accelerate the cleaning process, the aqueous acidic cleaner is often heated to as high as 180 deg C. Temperatures greater than the boiling point of the cleaner are used by keeping the cleaner under greater than ambient pressure. The hydrochloric acid is usually present in the cleaners in a concentration range of from 2 to 20% by weight, which, upon repealed use, can be quite damaging to the metal parts of the aforementioned units.
In order to protect metal components of equipment from the acidic cleaner during the cleaning cycle, corrosion inhibitors have been added to the acidic cleaning mixtures. Compositions that inhibit the attack of acid on metallic surfaces, but still allow dissolution of scale are known in the industry. Many suffer from the drawbacks of toxicity and/or are hazardous to the environment, e.g. arsenic containing inhibitors and petroleum based inhibitors such as those containing naphthalene derivatives.
Derivatives of rosin amines, such as those described in U.S. Pat. No. 2,758,970, incorporated herein by reference, are also known. A drawback of many known commercial rosin amine derivative acid inhibitor compositions is the use of HCl, liquid formaldehyde and acetone as raw materials in the process for making these prior art compositions, often in the presence of flammable solvent.
Each of these raw materials has drawbacks in manufacturing acid inhibitor compositions. HCl is a volatile, corrosive substance that is hazardous to use. HCl also contributes chloride ion, which makes the chloride carrying inhibitor composition unsuitable for some applications, such as nuclear reactor cleaning, due to corrosion concerns. Formaldehyde is a known carcinogen and the amount of residual monomer left in the rosin amine derivatives is regulated. Uninhibited liquid formaldehyde is unstable in the absence of added methanol and gives rise to health and safety concerns in manufacture. Acetone's low flash point makes it a manufacturing risk that requires special handling, as does the typical solvents used in making the prior art rosin amine derivatives. It has also been discovered by Applicants that residual acetone and formaldehyde, in some of the prior an acid inhibitors, participate in a side reaction to produce the toxic and flammable methyvinylketone (MVK), which has been misidentified in the past as methyethylketone (MEK).
Rosin amine derivatives typically used in the industry are also difficult to manufacture. Successful production of a commercially useful (non-solid and miscible in water) derivative requires a complex set of process steps that include first reacting the rosin amine with formaldehyde and a ketone, and then adding additional liquid formaldehyde and acetone followed by further reaction, and subsequent distillation of residual reactants and solvent. The use of HCL in the process requires a specialized reactor and distillation equipment. Undesirable chlorinated, side-reaction products have also been identified in the prior art rosin amine derivatives. Some known rosin amine derivatives also have drawbacks regarding flammability, for example, one known product has a flash point (cc) of 89 deg. F. Another limitation of known rosin amine derivatives is lack of homogeneity, where typical derivatives have limited stability and settle into two layers in the absence of the addition of surfactant and solvent.
Due in pan to the foregoing drawbacks, although known rosin amine derivatives have had some success in the industry, there is a continuing need for improved performance in the corrosion inhibitors, as well as improved stability. With increasing awareness of health, safety and environmental issues, the industry is requiring use of lower flammability, lower VOC raw materials, and users are demanding user friendly products, with low residual formaldehyde, with the same or better performance as known products. There is therefore a continued need for improved corrosion inhibitor compositions for corrosion inhibitor formulations used in acid cleaners. In particular, there is a need for corrosion inhibitor compositions that are simple to make, reduce the presence of VOCs and toxic and/or flammable raw materials, co-products, residual reactants and chloride ion. In addition, the replacement of ethoxylated phenol surfactants is a desired goal in any new inhibitor formulation due to recent environmental concerns.